Large areas of south-eastern Australia are swathed in smoke as some of the worst bush fires for nearly 70 years threaten mountain and country towns.
The fires in the state of Victoria, mostly in eastern alpine areas, have burned at least 180,000 hectares (445,000 acres) of drought-hit land.
There are fears that the blazes could merge into one "super fire".
Bush fires are common in Australia's hot summer months, but this year's are being described as exceptional.
People in Victoria are recalling the state's "Black Friday" in 1939, when 71 people died in fires.
No-one has been killed in the latest emergency, but firefighters say expected rising winds and high summer temperatures mean extreme danger through the weekend.
It is feared some of the fires, mostly sparked by lightning strikes, could burn for months.
The Australian army has been mobilised to back up local firefighters, who are also being helped by crews from beyond Victoria, as well as a specialist team from New Zealand.
The state government's environment spokeswoman, Rachaele May, said it was a "significant possibility" that all of the fires would eventually merge into one larger fire.
"It's the worst drought on record for Victoria, which means all the forest and grassland is extremely dry," she told the Australian Broadcasting Corporation.
Thick smoke has grounded aircraft used in operations to dump water on the flames, while smoke drifting hundreds of kilometres has blanketed the state capital, Melbourne, cutting visibility and disrupting passenger flights.
Australia's largest airline, Qantas, reported flight delays of up to an hour from Melbourne.
A flight from Los Angles was diverted to Sydney, while a domestic flight from Sydney was diverted to the national capital, Canberra, to refuel.
Nine people died in fires on South Australia state's Eyre Peninsula in January 2005.
In 2003, more than 500 houses were destroyed and four people killed when a huge fire tore through the capital, Canberra.